The news, which will be welcomed by conservationists fighting the slick, comes as BP began an attempt to permanently seal off the leaking well with a mixture of mud and cement.

"There's absolutely no evidence that there's any significant concentration of oil that's out there that we haven't accounted for," Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, the lead agency in producing the new report told the New York Times.

However, she said that the US government remained concerned about the ecological damage that has already occurred and the potential for more.

"I think we don't know yet the full impact of this spill on the ecosystem or the people of the gulf," Dr Lubchenco said.

Questions remained over the damage that the oil had done to the eggs and larvae of organisms like fish, crabs and prawns, she said.

The report was compiled by US federal scientists to work out where the huge volumes of leaked oil has gone.

It calculated that about 25 per cent of the chemicals in the oil evaporated at the surface or dissolved into seawater.

At least 5 per cent was burned on the surface, 3 per cent was skimmed and 8 per cent was broken down by dispersants.